Electrically programmable electronic load circuits provide specific load—that is the relationship between voltage and current values at a circuit's port—which can vary between a minimum and maximum values, according to a control signal pattern called the codeword.
FIG. 1 shows some fundamental quantities in a programmable electronic load L. FIG. 1 shows the electrically programmable load L with two terminals T1, T2 receiving a current I(s), which is associated with a voltage V(s) between the terminals T1, T2. The following relation can be defined:Z(s)=V(s)/I(s)Where Z(s)=impedance of an electrically programmable load L.
An essential feature of an electrically programmable load 1 is that the value of Z(s) depends on a codeword CW applied to the electronically programmable load L. The key points of electronically programmable loads are:                the type of load (resistive, capacitive, inductive, separate or mixed)        the range of load (minimum and maximum impedance values of the loads)        the load step or resolution, i.e. the steps with which the load impedance can be varied by the codeword.        
While the first point determines which type of load units have to be implemented, the latter two points jointly determine the number of load elements making-up the electronically programmable load.
FIG. 2 shows a prior art electronically programmable load, in the case of a parallel implementation, for which a Y representation (Y(s)=1/Z(s)=I(s)/V(s)) is more natural. A number N of parallel connected electronically programmable load units U(1), . . . , U(n), . . . , U(N), of a certain selected load type chosen is programmed such that each load unit assumes one of two possible values, a minimum value and a maximum value.
It is observed that, hereafter, sometimes reference is made to a load unit U, indicating anyone of these load units by U(n), n=1, 2, . . . N.
For a given load type and implementation choice of the load, the number:
                                          Y                          U              ,              max                                            Y                          U              ,              min                                      =        α                            (        1        )            where YU,max=maximum admittance of a load unit U and YU,min=minimum admittance of load unit U, is fixed for each load unit U(n) and can therefore be used in all subsequent calculations for load step and load range, in the prior art.
The load units U(n) can be arranged and/or switched following two approaches.